The present invention relates to a cross-talk canceler, and more particularly to a cross-talk canceler used in a signal reproducing unit for an optical disk.
In order to improve a recording density of an optical disk medium, there is a tendency to narrow the distance between adjacent recording tracks on the medium. On the other hand, there is a limit to lessen a diameter of a read light beam. For that reason, if the distance between the recording tracks is made exceedingly short , the read optical beam is irradiated on a part of the adjacent track with the result that a signal which has been recorded on the adjacent track is mixed into a reproduced signal as a cross-talk component.
A cross-talk canceler has been used as the technique of removing the inter-track cross-talk. For example, Japanese Patent Unexamined Publication No. Sho 64-49134 (JP-A-49134/1989) discloses the technique in which the cross-talk is removed by use of three optical beam consisting of one main beam and two sub-beams. In this conventional technique, there are provided a main detector for receiving a reflected light of a main beam which has been irradiated on a desired track and two sub-detectors for receiving reflected lights of two sub-beams which have been irradiated on the tracks adjacent to the desired track, respectively. Then, the delayed and gain-adjusted signals output from the two sub-detectors are subtracted from the delayed signal output from the main detector to thereby reduce the inter-track cross-talk. The amount of delay to be added to the respective output signals of the main detector and one of the sub-detectors must be strictly adjusted in accordance with the respective distances of the beam spots on the optical disk and the rotational speed of the optical disk. Therefore, in the conventional technique, it is necessary to adjust the amount of delay for such detectors when manufacturing. Further, the respective distances of the main beam and the sub-beams are changed as a result of change in the passage of time of optical components within the optical head, whereby the optimum amount of delay is changed. Consequently, it is required to periodically readjust the amount of delay for the respective detectors.